Tilt sensors are devices that are used to measure angular displacement relative to a reference. Tilt sensors are used in a wide variety of industrial and transportation applications for measuring inclinations and accelerations. Tilt sensors are not typically used in low-cost consumer applications because current tilt sensors are relatively complex and expensive.
Tilt sensors used to detect angular inclination or displacement with respect to a horizontal reference are known as inclinometers. The reference is typically supplied by the gravitational pull of the earth or by the angular momentum vector of a rapidly rotating mechanism. Inclinometers typically comprise a fixed element that is rigidly mounted to a piece of equipment whose inclination is to be measured, a reference element that maintains a constant orientation with respect to a reference, a sensor that measures the angular displacement between the fixed and reference elements, and a suspension system that supports the reference element while allowing relative rotation between the elements.
One common type of inclinometer, the gyroscopic inclinometer, relies on the angular momentum vector of a rapidly rotating mechanical part to provide a reference orientation. Gyroscopic inclinometers require a mechanically complex suspension for the rotating part and are, therefore, expensive. Inclinometers that rely on gravity to maintain a reference orientation typically use a suspension system including bearings that allow the reference element to continue to point downward as the orientation of the fixed element changes. A suspension system utilizing bearings that allow rotation in more than one axis is also complex and expensive.
The angular displacement between the element fixed with respect to the equipment and the reference element can be sensed in a variety of ways. For example, in optical inclinometers, a beam of light typically originates in the fixed element and is reflected by the reference element. The reference element may be, for example, a pendulum having a reflective surface. By using photodetectors to determine the resulting direction of the reflected light beam, the angular displacement between the fixed element and the reference element can be determined. Such inclinometers are relatively complex, requiring a light source and multiple photodetectors.
Capacitive inclinometers typically utilize conductive plates as part of the fixed element. The reference element is located between the plates of the fixed element. Changing the angular displacement of the reference element with respect to the plates changes the dielectric constant of the space between, and therefore the capacitance of, the plates. The change in capacitance is detected and converted to a corresponding tilt angle.
For example, as a pendulum suspended partly between the conductive plates pivots into or out from the space between the plates, the capacitance of the plates changes. Similarly, a fluid may partly fill the space between the plates, and the capacitance will change as the fluid-filled area of the plates changes. Another capacitive inclinometer uses a magnetically levitated ball suspended between four conductive plates. As the device is tilted, the equilibrium position of the suspended ball changes in relationship to the four plates, causing the capacitance of the capacitors defined by opposing plates to change. Capacitive sensors typically require relatively complex circuitry to convert the change in capacitance to a corresponding change in tilt angle and a relatively complex mechanical suspension system to maintain the reference element between the plates without touching the plates.
Because of the relative complexity of sensing technologies and of methods of suspending the reference element within the fixed element, inclinometers are costly and restricted to industrial applications. Such inclinometers are too complex and expensive to be mass produced for use in consumer applications.